President Donald Trump signed an executive order on Tuesday compelling states to require voters to show proof of citizenship when voting.

The executive order is expected to be challenged in court.

While many states have enacted laws requiring voters to produce a driver's license or state identification card when voting, this order goes one step further, requiring such documents to be Real ID-compliant.

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Generally, standard driver's licenses and state identification cards do not prove a person is a citizen.

Options for voters to meet President Trump's order include a birth certificate, passport, military ID, or naturalization documents, in addition to a Real ID-compliant state ID.

State laws on voter identification vary across the U.S. Currently, 14 states have no requirement regarding identification. The National Conference of State Legislatures says that 12 states have "strict" laws regarding voter identification. Other states have less strict requirements. In many of these states, voters who do not come to the polls with a valid ID can submit a provisional ballot after officials check the signature.

The Brennan Center for Justice is among groups saying President Trump's order will be challenged in court. The organization said that the president does not have the authority to issue such an executive order and that the order "would hurt voters and suppress the vote."

President Trump claims that the order is necessary to stop non-citizens from voting.

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"Above all, elections must be honest and worthy of the public trust. That requires voting methods that produce a voter-verifiable paper record allowing voters to efficiently check their votes to protect against fraud or mistake. Election-integrity standards must be modified accordingly," the order reads.

The Brennan Center said it conducted a thorough audit of the 2016 election and found that improper noncitizen votes accounted for 0.0001.

"The absence of fraud reinforces a wide consensus among scholars, journalists, and election administrators: voter fraud of any kind, including noncitizen voting, is rare," the group said.

The new executive order would also require states to have all mail-in ballots collected by Election Day. Currently, many states accept ballots postmarked before election day to be received in the days following the election.